The present invention relates to a robotic inspection system for in situ inspection of gas turbine cannular combustion components for the purpose of evaluating the condition of the components.
Maintenance costs and equipment availability are two of the most important concerns of a gas turbine operator. Proper maintenance is required to minimize equipment downtime and provide long-term reliable operation. Maintenance inspections of gas turbines are broadly classified as standby, running and disassembly. Disassembly inspections are generally categorized into three types: combustion inspection, hot gas path inspection and major inspection. All three types of inspections require shutdown and disassembly of the turbine to varying degrees to enable inspection and replacement of aged and worn components. The combustion inspection includes evaluation of several components of the combustion system including the transition piece. The transition piece is a thin-walled duct used to conduct high-temperature combustion gases from the combustion chamber to the annular turbine nozzle passage. The transition piece and other combustion components are generally inspected for foreign objects, abnormal wear, cracking, thermal barrier coating TBC condition, oxidation/corrosion/erosion, hot spots/burning, missing hardware and clearance limits. Components which fall outside established threshold limits are replaced to maintain optimum operating conditions for the entire system. If not rectified, these conditions could lead to reduced machine efficiency and damage to the turbine that may result in unplanned outages and significant repair costs.
Removal and installation of transition pieces is the most time-intensive operation of the combustion inspection. This operation contributes most significantly to the combustion inspection outage duration and corresponds directly to time lost producing power. To remove transition pieces, all upstream components must be removed, i.e., fuel nozzles, water injectors and various other hardware. Each transition piece is then dismounted and removed one by one in sequence through two access openings in the turbine casing. It will be appreciated that for certain gas turbines, there can be as many as fourteen transition pieces requiring removal.
To date, recommended practice has been to remove the transition pieces and other combustion components to facilitate inspection and refurbishment. Inspection has consisted primarily of visual methods consisting of the unaided eye with auxiliary lighting. Visual methods in known problem areas have been enhanced with the use of liquid red dye penetrant to improve visibility of small hairline cracking. These inspections have typically been performed offline of the combustion inspection process. Such prior inspection practices have many disadvantages, including the time required for disassembly and installation, the lack of direct retrievable defect data for engineering evaluation and historical comparison and complete reliance on human factors. Accordingly, there is a need for more efficient methods to inspect the transition pieces of the gas turbine combustion systems to minimize outage times while providing an accurate assessment of the condition of each transition piece.
In accordance with a preferred embodiment of the present invention, there is provided a robotic inspection system for gas turbine combustion components comprised of three robotic manipulators with miniature cameras and lighting for inspecting various parts of the transition piece of each combustor in situ. The manipulators are driven remotely using a combination of automated and manual motion control to position the inspection heads, e.g., video cameras, lighting and/or measuring devices, to various locations about and in the combustor enabling a detailed visual inspection of its transition piece and flow sleeve without disassembly and removal of these components from the turbine. The robotic inspection system hereof is thus intended for use during a gas turbine maintenance outage.
Particularly, the robotic inspection system hereof includes three tools, i.e., an exterior manipulator, an interior manipulator and an annulus manipulator. It will be appreciated that the transition piece includes an outer impingement sleeve, typically perforated, and an interior transition piece body defining generally an annulus therebetween. The forward ends of the transition piece body and impingement sleeve are generally circular in configuration with top and bottom sides being flattened progressively toward the first-stage nozzle. The exterior manipulator is deployed for inspection of the external surfaces of the impingement sleeve and has seven distinct motions. The exterior manipulator includes a segmented arcuate rail movably mounted on a carriage disposed within the casing of the turbine, the carriage being supported externally of the casing by a mast. When all of the arcuate rail segments are connected end-to-end to one another, the rail extends in excess of 90xc2x0 such that an inspection head forming part of a robotic inspection subassembly carried on an end segment can inspect top, bottom and side surfaces and along the entire length of each impingement sleeve in a quadrant of the annularly arranged combustors.
The robotic inspection subassembly on the end segment mounts a generally axially extending rail on which is mounted an upper arm. The rail is movable in a circumferential direction with the arcuate segments as the latter are displaced circumferentially along the carriage to locations radially outwardly of the impingement sleeves and within the interior surface of the casing. The upper arm is pivotable relative to the rail about a first axis to extend between adjacent impingement sleeves and carries at its distal end a pivotally mounted forearm. The upper arm is also rotatable about its long axis such that when the forearm is extended, the inspection head carried at the distal end of the forearm can be located between and radially inwardly of an impingement sleeve for inspection of its radial inner surface. The inspection head is rotatable about pan and tilt axes relative to the forearm and includes a vision module, e.g., one or more cameras and a lighting system. With this arrangement, the inspection head can be located to inspect the entire peripheral surface of each impingement sleeve of the cannular combustion system. A video micrometer external to the tool may be used in conjunction with the vision module to effect measurements.
The interior manipulator is mounted to the aft combustion casing for inspecting the interior surface of the transition piece body. The interior manipulator includes an elongated arm carried in a spherical bearing in a mount secured to the casing flange. The interior end of the arm carries an inspection head similar to that of the exterior manipulator. The arm projects through the mount exteriorly of the casing and is pivoted by two linear actuators coupled between the mount and the arm to locate the inspection head adjacent the interior surface of the transition piece body. The arm also carries concentric inner and outer tubes. Actuation of an electric motor carried by the outer tube extends and retracts the inner tube carrying the inspection head. The inner tube carries pan and tilt motors such that the inspection head can be rotated about pan and tilt axes for visual inspection of the interior surfaces of the transition piece body.
The annulus manipulator includes a manually positioned inspection head for inspecting the side seam welds along the exterior surface of the transition piece body in the annulus between the transition piece body and the impingement sleeve. The annulus manipulator includes a support structure for supporting a pair of spaced guide plates each having a pair of contoured surfaces, e.g., grooves in opposition to one another. The grooves generally correspond to the contours of the side seam welds of the transition piece body. A middle carriage plate carries sets of pins on opposite sides thereof engaging in the grooves and is movable longitudinally along the guide plates. The middle carriage plate also carries side carriage plates for movement along respective laterally facing external surfaces of the guide plates. Each side carriage plate carries a holder for a wand tube which carries the inspection head. With the annulus manipulator located within the casing and the wand tube secured to one of the wand carriers, the side carriage plates are advanced toward the transition piece body by manually advancing the wand tube. As the side carriage plates are advanced, they follow the contour of the grooves which enables the inspection head to follow the contour of a side seam weld. Thus, by positioning the inspection head relative to the annulus manipulator, the inspection head can be located directly adjacent a side seam weld of the transition piece body and displaced lengthwise along the transition piece body thereby following and registering with the contour of the weld.
It will be appreciated that the cameras for the inspection heads can be remotely and dynamically focused from a remote control station. To accomplish this, motorized cam assemblies are utilized that move the camera lens. Additionally, a video micrometer subsystem is used to quantitatively dimension features appearing in the video imagery. For example, a pair of laser lights at a fixed distance apart are incorporated into the inspection head of the interior robotic manipulator. The lasers provide a known size feature used to calibrate the video micrometer for any camera field of view. A similar process may be used for the exterior manipulator, although known size features of the transition piece body are used as the calibration reference rather than lasers.
In a preferred embodiment according to the present invention, there is provided a method of inspecting in situ an impingement sleeve of a combustor of an annular array of combustors in a gas turbine wherein the turbine has an outer casing about an axis of rotation of a turbine rotor and at least one opening through the casing for access to the impingement sleeve, comprising the steps of inserting a robotic inspection tool carrying an inspection head through the opening in the outer casing, robotically manipulating the tool from a location external of the casing to locate the inspection head between adjacent impingement sleeves, inspecting the exterior surface of one of the adjacent impingement sleeves using the inspection head and after completion of the inspection, withdrawing the inspection tool from within the outer casing.
In a further preferred embodiment according to the present invention, there is provided a method of inspecting in situ an interior of a transition piece body of one or more of a plurality of an annular array of combustors for a gas turbine, comprising the steps of securing a mount of an interior robotic manipulator to an open end of a combustion casing forwardly of one of the transition piece bodies, the manipulator having an elongated inspection arm extending from the mount, locating an inspection head carried adjacent an end of the inspection arm remote from the mount within the one transition piece body, manipulating the inspection arm to locate the inspection head adjacent interior wall portions of the one transition piece body including by displacing the inspection head in a generally axial direction and generally radially toward a wall portion of the transition piece body to be inspected.
In a still further preferred embodiment according to the present invention, there is provided a method of inspecting in situ side seam welds along a transition piece body spaced inwardly of an impingement sleeve of a combustor in a combustion system for a gas turbine, comprising the steps of providing a guide having a contoured surface generally corresponding to the contour of the side seam weld of the transition piece body, fixing the guide to the combustor and displacing an inspection head longitudinally along the space between the impingement sleeve and the transition piece body so that the inspection head tracks the contoured surface of the guide whereby the inspection head is maintained during its longitudinal displacement in registration with the side seam weld of the transition piece body.